New preview of IE 10 focuses on HMTL 5 progress

Developers can now get a look at Microsoft's new browser prototype, Internet Explorer 10 platform preview 2, whose main purpose is to demonstrate progress on testing HTML 5.

This platform preview runs alongside other IE browser installations and illustrates what's to come in the final product, mostly for the benefit of Web developers. Platform preview 2 can be downloaded at Microsoft's test drive site here. The preview lacks the true functionality of a browser, but it shows Microsoft's technical progress to date.

Microsoft released the first version of IE 10 platform preview in April, and is committed to future platform preview releases every 12 weeks or so. Possibly, platform preview 3 will appear near the end of October, according to that schedule.

New FeaturesMicrosoft provides a Guide for Developers on the improvements to be found in the IE 10 platform preview 2. As of June 29, 2011, Microsoft highlighted these improvements in the new preview:

The IE 10 platform preview 2 now supports "HTML5 Sandbox and iframe isolation," which will improve the security of Web applications, according to Dean Hachamovitch, corporate vice president of Internet Explorer, in Microsoft's announcement.

The new HTML 5 Web Workers feature in the preview enables Web applications to off-load JavaScript processes. Doing so can help improve the frame rates in animations. Microsoft provides a fountain demo in IE 10 platform preview 2 showing how that works, but it has also lodged a complaint at the Worldwide Web Consortium (W3C) about security implications when third-party presences on websites are able to access the Web Workers information.

Hachamovitch claims that "IE10 is the first browser to support several new performance APIs coming out of the W3C's working groups." Those APIs supported in this platform preview 2 include requestAnimationFrame, Page Visibility and setImmediate.

The HTML 5 spec isn't a W3C final recommendation quite yet, but stable features in it are being implemented by browser makers. Currently, the HTML 5 spec is at the W3C's Last Call review stage, having reached that point in May. Last Call is a final stage for reporting bugs and will end on Aug. 2.

Microsoft advocates that Web developers create "sniffer" code on their sites to check whether the visiting browser will support a particular HTML 5 feature, rather than checking for a user's browser version. The company doesn't support all of the features proposed before the W3C HTML 5 Working Groups. For the ones that seem promising but yet are still considered unstable for public use, Microsoft provides its HTML5 Labs resource page for developers to do testing work.

Same Markup

Supposedly, the same HTML 5 markup is supported by both Microsoft and other browser makers, who follow the same W3C spec when building their browser engines. However, Microsoft typically demonstrates the shortcomings of other browsers in running the platform preview tests, which were devised by Microsoft and contributed to the W3C.

For this second platform preview of IE 10, Microsoft devised "270 new test cases," adding to a grand total so far of 6,669 submitted test cases, according to a Microsoft IE test center page description.

Hachamovitch claimed in Microsoft's announcement that "HTML5 is the first version of HTML to define the behavior of invalid markup." He added that, "rather than relying on 'fix-up' rules that vary from browser to browser, HTML5 parsing behavior is now specified in a way that developers can count on it."

Microsoft hasn't disclosed when the final IE 10 browser will be released. It could be tied to Windows 8's release, since Microsoft typically associates the lifecycles of its browsers with a particular Windows release. However, the release dates of Microsoft's browsers and associated Windows operating systems haven't always corresponded in the past.

If a tip given to veteran Microsoft observer Mary-Jo Foley proves true -- that Windows 8 will be released to manufacturers in April 2012 -- IE 10 could appear in its final form somewhat near that April 2012 time frame. IE 10, when released, will run on Windows 7 (and presumably Windows 8), but it will not run on Vista.